Cartridges for feeding ink in fountain pens have been known in the art particularly as represented by U.S. Pat. No. 3,532,436 (Koenig) and U.S. Pat. No. 3,521,969 (Mutschler). These cartridges have generally taken the form of a nipple-like end which is adapted to extend over a pin or stud and extends into a casing on the side remote from a feed bar. The fitting of the cartridge, made of plastics material, over a protruding part is solely limited by the friction of the cartridge engaging type stud, for example. As is well known, all deformable materials tend to lose their resiliency and in time with structures of this nature leakage can occur.